The present invention relates to an optical wireless communication system for data communication using light or like optic means wherein the data is transmitted among a plurality of units which are provided and placed in separate locations in a large room or in a plurality of rooms.
The optical wireless type communication is suitable for in-house communication wherein the units can be moved to other locations and the lay-out thereof can be readily varied in format. This type communication does not use any cable, optical fiber or like means to transmit data from one unit to another. In the matter of such optical wireless communication, light is radiated in the air for data communication, so that in case a plurality of units are provided and dispersed within a large room or in a plurality of rooms, optical signals may not reach all the units or may be cut off and it may be impossible to accomplish transmitting/receiving operations. Accordingly, in this type of communication system, there is employed an optical signal repeater which is provided in a relatively high position such as at the ceiling so as to receive optical signals transmitted from each of the units and to transmit the optical signals to other units. In this connection, it is to be noted that the plurality of units for data communication include office computers and terminals therefor, point of sale (POS) terminals and other various devices for in-house data communication. For the sake of convenience, these units will be called terminals in this specification.
As prior art of the optical wireless communication system, there has been proposed an invention disclosed in Japanese Patent Application No. 251925/83, which is a patent application submitted from Fujitsu Limited, under the names of Kenjiro Yano and others, entitled "Optical Wireless Communication System". In this prior art, an optical signal transmitted from any one of several terminals is temporarily sent to a control device by means of optical repeaters and is transmitted from the control device to all of the terminals by means of the optical repeaters. At the start of the sending data, the address of destination for the data is included, so that each terminal can receive the data after determining whether or not the data is to be transmitted and received by the specific terminal.
One drawback of the above-mentioned prior art is that the sending data is temporarily sent to the control device and is then transmitted to the terminal from such control device, so that the intercommunication among the terminals becomes impossible when the control device is defective or becomes inoperable.
Additionally, in the specification of the above-mentioned prior art, the description states that optical wireless communication means may be employed for data transmission between the optical repeaters and the control device. However, the use of such optical wireless communication means for data transmission between the optical repeaters and the control device presents a problem in that a signal sent from a repeater interferes with a signal sent from the control device between the repeater which transmits data to the control device and the control device which returns the data to the repeater. The interference between signals may sometimes result in an error in communication.
Additional documentation in the area of wireless communication includes U.S. Pat. No. 3,511,998, issued to M. I. Smokler on March 18, 1966, which discloses a method and means for initiating communication between two small-angle communication equipments capable of transmitting and receiving radiant energy at first and second frequencies.
U.S. Pat. No. 3,710,122, issued to E. E. Burcher et al. on January 9, 1973, discloses a laser remote control system that includes a transmitter with oscillators of different frequencies, a receiver that includes a light collector and a tuned circuit for each frequency, and an autotracker that includes a reflector at the receiver
U.S. Pat. No. 3,810,255, issued to M. R. Wachs et al. on May 7, 1974, discloses a multi-spot beam transponder with means for connecting any band of any receive beam to any band of any transmit beam.
U.S. Pat. No. 4,150,334, issued to J. W. Williams on April 17, 1979, discloses a radio repeater control circuit that prevents voice signals from interfering with information signals when both signals are simultaneously repeated or transmitted together.
U.S. Pat. No. 4,207,521, issued to M. Takada on June 10, 1980, discloses a radio communication system comprising a transmitting station for transmitting output signals in a first common frequency, a repeater station for retransmitting the signals in a second common frequency, and a receiver station for receiving the retransmitted signals.
U.S. Pat. No. 4,402,090, issued to F. R. Gfeller et al. on August 30, 1983, discloses a communication system in which data are transmitted between terminal stations and satellite stations by infrared signals. All satellites are connected to the host by a common bus arrangement.
U.S. Pat. No. 4,664,518, issued to C. E. Pfund on May 12, 1987, discloses a secure communication system that uses narrow beam laser transmission between an orbiting satellite and another station.
And, U.S. Pat. No. 4,709,411, issued to K. Mori on November 24, 1987, discloses an optical communication system that includes a plurality of remote apparatuses which exchange optical signals with each other and wherein each apparatus includes a transmitter section and a receiver section disposed in a common housing.